1. Field of the Invention
The present invention relates to communications, and, in particular, to cellular telecommunication systems.
2. Description of the Related Art
A typical cellular telecommunication system has one or more mobile switching centers (MSCs), for example, located in the central offices of a company that provides telecommunication services, where each MSC controls the operations of multiple cell sites. A cell site (also referred to as a cell) corresponds to a set of co-located uplink and downlink antennas that support communications with the mobile units (e.g., cellular telephones) currently located within a coverage area around the cell site. The locations of cell sites are preferably distributed to provide contiguous coverage over a relatively wide telecommunication service region. In order to ensure this contiguous coverage, cell sites are positioned such that their coverage areas overlap to some extent with the coverage areas of adjacent cell sites. This overlapping also enables a mobile user to move from one cell site to another without losing telecommunication service. This process is referred to as a handoff, as the responsibility for communicating with the mobile unit is handed off (i.e., transferred) from one cell site to the other.
One type of cellular system uses both frequency division multiple access (FDMA) and time division multiple access (TDMA) communication techniques. Such a cellular system is typically assigned two different frequency bands for its communications: one for downlink communications from the cell sites to the mobile units and the other for uplink communications from the mobile units to the cell sites. Pursuant to FDMA schemes, each frequency band is divided into multiple frequency sub-bands called channels. Pursuant to TDMA schemes, communications on each channel are time-multiplexed into different periodic time slots. When communications are to be established between a cell site and a mobile unit located within the coverage area of the cell site, the mobile unit is assigned a particular channel and time slot in each of the downlink and uplink frequency bands within which signals to and from the mobile unit are to be transmitted. Responsibility for assigning channels and time slots rests with the MSC, which is constantly receiving information from and transmitting instructions to its cell sites.
In typical cellular systems, when a new cell is deployed or a new sector on an existing cell is configured, neighbor cells and sectors must be identified for the new cell or sector. In addition, existing cells must be reconfigured to identify the new cell or sector as a neighbor. This process is necessary to allow correct operation of both handoff and control channel reselection processes such as those described in the IS-136 TDMA Standard. Handoff processes use neighbor information to help decide the most appropriate sector or cell to serve a call. Control channel reselection processes use similar neighbor information to determine which cell an idle mobile (one powered-up, but not active on a call) will monitor to receive incoming calls and other mobile services.
A typical cellular system today must rely on manual entry by a technician of neighbor information associated with each cell. This information typically consists of the channel number of a beacon on the neighbor sector or cell. This channel is active at all times and is monitored by mobiles on neighbor cells. The signal strength may be reported back to the serving cell site in Mobile Assisted Channel Allocation (MACA) and Mobile Assisted Handoff (MAHO) processes, or may be used internally by the mobile in Control Channel Reselection processes.
If channel numbers corresponding to neighbor beacon channels were the only information needed to identify neighbors, configuration of cellular and PCS systems would not be terribly burdensome to service providers. However, typically at least a dozen additional parameters need to be specified for each neighbor sector. These parameters include indicators that support hierarchical cells (such as a "preferred," "regular," or "non-preferred" neighbor designation), signal-strength thresholds that determine whether a mobile is allowed to access or be handed off to a neighbor cell, timer parameters that specify how long the signal strength must be at acceptable levels before access on the neighbor cell is permitted, and indicators of what services are supported on a particular neighbor.
With the maturation of cellular systems, indicators of advanced service support on neighbor cells becomes particularly burdensome for the service provider to configure and identify. This is because multiple advanced services such as private system support, fax and data capability, and short message service must each be identified on a per-neighbor basis. This per-neighbor identification allows, for example, handoff algorithms to preferentially maintain mobiles on cells that support a particular service such as a specific private system.